A traditional metal lead frame may be manufactured typically by one of the following four methods.
1) Punching is performed on a metal sheet from top to down or from down to top in a longitudinal way by a punching technology with a mechanical upper and lower tool, to form a pad carrying a chip, inner pins for signal transmission and outer pins for connecting to an outside PCB of a lead frame inside of the metal sheet, then a metal electroplated layer is then coated on certain areas of the inner pins and (or) the pad, to form a finished lead frame which can be used (with reference to FIG. 70 to FIG. 72).
2) Exposing, developing, windowing and chemical etching are performed on a metal sheet by a chemical etching technology, to form a pad carrying a chip, inner pins for signal transmission and outer pins for connecting to an outside PCB of a lead frame inside of the metal sheet, then a metal electroplated layer is then coated on certain areas of the inner pins and (or) the pad, to form a finished lead frame which can be used (with reference to FIG. 73 and FIG. 74).
3) Based on the first method and the second method, in a third method, a high-temperature adhesive film resistive to 260 Celsius degrees is applied onto a back face of the lead frame in which the pad carrying the chip, the inner pins for signal transmission and the outer pins for connecting to the outside PCB are disposed and the metal electroplated layer is coated on the certain areas of the inner pins and (or) the pad, to form a lead frame which can be packaged in a way of no pin at four sides and in a way of reducing a package size (with reference to FIG. 75).
4) By using the first method and the second method, in a fourth method, the lead frame, in which the pad carrying the chip, the inner pins for signal transmission and the outer pins for connecting to the outside PCB are disposed and the metal electroplated layer is coated on the certain areas of the inner pins and (or) the pad, is prepackaged, and thermosetting epoxy resin is filled inside regions of the metal sheet where the punching is performed or the chemical etching is performed, to form a pre-filler lead frame which can be packaged in a way of no pin at four sides, in a way of reducing a package size and in a way of copper wire bonding (with reference to FIG. 76).
The traditional method has the following disadvantages.
1) Lead Frames Produced by Mechanical Punching
a. In mechanical punching, the upper and lower tool is used to perform punching from top to down or from down to top, so as to form a vertical cross section, therefore it is unable to add other functions or embody other objects inside of the lead frame, such as, objects of the system desired to be integrated in the metal lead frame;
b. In mechanical stamping, the upper and lower tool is used to press edges of the metal sheet to form an extended metal area, and the length of the extended metal area due to the press is at most 80 percent of the thickness of the lead frame. In a case that the length of the extended metal area is greater than 80 percent of the thickness of the lead frame, the extended metal area due to the press is easy to occur problems such as warp, crack and break, irregular shape and surface pores, and an ultra-thin lead frame is more easy to result in the above problems (with reference to FIG. 77 and FIG. 78); and
c. In a case that the length of the metal area extended by the mechanical stamping is less than or equal to 80 percent of the thickness of the lead frame, objects can not be disposed in the extended metal area since the length of the extended metal area is not enough (especially in a case that the lead frame has a ultra-thin thickness) (with reference to FIG. 79 and FIG. 80).
2) Lead Frames Produced by the Chemical Etching Technology
a. In subtracting etching, half etching technology may be used to etch space of objects required to be embedded, however, the biggest disadvantages thereof is that the depth of the etching and flatness of a plane formed after the etching are uncontrollable.
b. After the space of objects required to be embedded are formed in the metal sheet by the half etching, strength of the structure of the lead frame becomes soft, which will have a direct influence on difficulty of working conditions (for example, pick-and-place, transport, high temperature, high pressure and thermal stress shrinkage) required when an object is embedded subsequently; and
c. In the lead frame produced by the chemical etching technology, at most an outer lead pattern or an inner lead pattern on a front face and a back face of the lead frame are presented, it is unable to present system-in-package metal lead frame of multi-layer three-dimensional metal circuit.